Add cloudId builder to the HLRC (#47868)

Elastic cloud has a concept of a cloud Id. This Id is a base64 encoded
url, split up into a few parts. This commit allows the user to pass in a
cloud id now, which is translated to a HttpHost that is defined by the
encoded parts therein.

client/rest/src/main/java/org/elasticsearch/client/RestClient.java

@@ -56,6 +56,7 @@ import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Base64;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -73,6 +74,7 @@ import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Collectors;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Collections.singletonList;
 
 /**
@@ -119,6 +121,34 @@ public class RestClient implements Closeable {
         setNodes(nodes);
     }
 
+    /**
+     * Returns a new {@link RestClientBuilder} to help with {@link RestClient} creation.
+     * Creates a new builder instance and sets the nodes that the client will send requests to.
+     *
+     * @param cloudId a valid elastic cloud cloudId that will route to a cluster. The cloudId is located in
+     *                the user console https://cloud.elastic.co and will resemble a string like the following
+     *                optionalHumanReadableName:dXMtZWFzdC0xLmF3cy5mb3VuZC5pbyRlbGFzdGljc2VhcmNoJGtpYmFuYQ==
+     */
+    public static RestClientBuilder builder(String cloudId) {
+        // there is an optional first portion of the cloudId that is a human readable string, but it is not used.
+        if (cloudId.contains(":")) {
+            if (cloudId.indexOf(":") == cloudId.length() - 1) {
+                throw new IllegalStateException("cloudId " + cloudId + " must begin with a human readable identifier followed by a colon");
+            }
+            cloudId = cloudId.substring(cloudId.indexOf(":") + 1);
+        }
+
+        String decoded = new String(Base64.getDecoder().decode(cloudId), UTF_8);
+        // once decoded the parts are separated by a $ character
+        String[] decodedParts = decoded.split("\\$");
+        if (decodedParts.length != 3) {
+            throw new IllegalStateException("cloudId " + cloudId + " did not decode to a cluster identifier correctly");
+        }
+
+        String url = decodedParts[1]  + "." + decodedParts[0];
+        return builder(new HttpHost(url, 443, "https"));
+    }
+
     /**
      * Returns a new {@link RestClientBuilder} to help with {@link RestClient} creation.
      * Creates a new builder instance and sets the hosts that the client will send requests to.

client/rest/src/test/java/org/elasticsearch/client/RestClientBuilderTests.java

@@ -26,8 +26,10 @@ import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
 import org.apache.http.message.BasicHeader;
 
 import java.io.IOException;
+import java.util.Base64;
 
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
@@ -159,6 +161,38 @@ public class RestClientBuilderTests extends RestClientTestCase {
         }
     }
 
+    public void testBuildCloudId() throws IOException {
+        String host = "us-east-1.aws.found.io";
+        String esId = "elasticsearch";
+        String kibanaId = "kibana";
+        String toEncode = host + "$" + esId + "$" + kibanaId;
+        String encodedId = Base64.getEncoder().encodeToString(toEncode.getBytes(UTF8));
+        assertNotNull(RestClient.builder(encodedId));
+        assertNotNull(RestClient.builder("humanReadable:" + encodedId));
+
+        String badId = Base64.getEncoder().encodeToString("foo$bar".getBytes(UTF8));
+        try {
+            RestClient.builder(badId);
+            fail("should have failed");
+        } catch (IllegalStateException e) {
+            assertEquals("cloudId " + badId + " did not decode to a cluster identifier correctly", e.getMessage());
+        }
+
+        try {
+            RestClient.builder(badId + ":");
+            fail("should have failed");
+        } catch (IllegalStateException e) {
+            assertEquals("cloudId " + badId + ":" + " must begin with a human readable identifier followed by a colon", e.getMessage());
+        }
+
+        RestClient client = RestClient.builder(encodedId).build();
+        assertThat(client.getNodes().size(), equalTo(1));
+        assertThat(client.getNodes().get(0).getHost().getHostName(), equalTo(esId + "." + host));
+        assertThat(client.getNodes().get(0).getHost().getPort(), equalTo(443));
+        assertThat(client.getNodes().get(0).getHost().getSchemeName(), equalTo("https"));
+        client.close();
+    }
+
     public void testSetPathPrefixNull() {
         try {
             RestClient.builder(new HttpHost("localhost", 9200)).setPathPrefix(null);